Problem: Simplify the following expression: $k = \dfrac{6x^2 + 4x}{12yx} - \dfrac{8x^2 - 4zx}{12yx}$ You can assume $x,y,z \neq 0$.
Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{6x^2 + 4x - (8x^2 - 4zx)}{12yx}$ $k = \dfrac{-2x^2 + 4x + 4zx}{12yx}$ The numerator and denominator have a common factor of $2x$, so we can simplify $k = \dfrac{-x + 2 + 2z}{6y}$